Apply attributes to the underlying HTTP request

See gh-29958

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultClientRequestBuilder.java

@@ -265,6 +265,12 @@ final class DefaultClientRequestBuilder implements ClientRequest.Builder {
 					requestCookies.add(name, cookie);
 				}));
 			}
+
+			Map<String, Object> requestAttributes = request.getAttributes();
+			if (!this.attributes.isEmpty()) {
+				this.attributes.forEach((key, value) -> requestAttributes.put(key, value));
+			}
+
 			if (this.httpRequestConsumer != null) {
 				this.httpRequestConsumer.accept(request);
 			}

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultWebClientBuilder.java

@@ -89,6 +89,8 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 	@Nullable
 	private MultiValueMap<String, String> defaultCookies;
 
+	private boolean applyAttributes;
+
 	@Nullable
 	private Consumer<WebClient.RequestHeadersSpec<?>> defaultRequest;
 
@@ -137,6 +139,7 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 
 		this.defaultCookies = (other.defaultCookies != null ?
 				new LinkedMultiValueMap<>(other.defaultCookies) : null);
+		this.applyAttributes = other.applyAttributes;
 		this.defaultRequest = other.defaultRequest;
 		this.statusHandlers = (other.statusHandlers != null ? new LinkedHashMap<>(other.statusHandlers) : null);
 		this.filters = (other.filters != null ? new ArrayList<>(other.filters) : null);
@@ -200,6 +203,12 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 		return this;
 	}
 
+	@Override
+	public WebClient.Builder applyAttributes(boolean applyAttributes) {
+		this.applyAttributes = applyAttributes;
+		return this;
+	}
+
 	private MultiValueMap<String, String> initCookies() {
 		if (this.defaultCookies == null) {
 			this.defaultCookies = new LinkedMultiValueMap<>(3);
@@ -335,21 +344,24 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 	}
 
 	private ClientHttpConnector initConnector() {
+		final ClientHttpConnector connector;
 		if (reactorNettyClientPresent) {
-			return new ReactorClientHttpConnector();
+			connector = new ReactorClientHttpConnector();
 		}
 		else if (reactorNetty2ClientPresent) {
 			return new ReactorNetty2ClientHttpConnector();
 		}
 		else if (jettyClientPresent) {
-			return new JettyClientHttpConnector();
+			connector = new JettyClientHttpConnector();
 		}
 		else if (httpComponentsClientPresent) {
-			return new HttpComponentsClientHttpConnector();
+			connector = new HttpComponentsClientHttpConnector();
 		}
 		else {
-			return new JdkClientHttpConnector();
+			connector = new JdkClientHttpConnector();
 		}
+		connector.setApplyAttributes(this.applyAttributes);
+		return connector;
 	}
 
 	private ExchangeStrategies initExchangeStrategies() {

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/WebClient.java

@@ -250,6 +250,13 @@ public interface WebClient {
 		 */
 		Builder defaultCookies(Consumer<MultiValueMap<String, String>> cookiesConsumer);
 
+		/**
+		 * Global option to specify whether or not the request attributes should be applied
+		 * to the underlying http-client request, if the used {@link ClientHttpConnector} allows it.
+		 * @param applyAttributes whether or not to apply the attributes
+		 */
+		Builder applyAttributes(boolean applyAttributes);
+
 		/**
 		 * Provide a consumer to customize every request being built.
 		 * @param defaultRequest the consumer to use for modifying requests

spring-webflux/src/test/java/org/springframework/web/reactive/function/client/WebClientIntegrationTests.java

@@ -34,14 +34,18 @@ import java.time.Duration;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import io.netty.util.Attribute;
+import io.netty.util.AttributeKey;
 import okhttp3.mockwebserver.MockResponse;
 import okhttp3.mockwebserver.MockWebServer;
 import okhttp3.mockwebserver.RecordedRequest;
+import org.eclipse.jetty.client.Request;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Named;
 import org.junit.jupiter.api.Test;
@@ -50,6 +54,7 @@ import org.junit.jupiter.params.provider.MethodSource;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.core.publisher.Sinks;
+import reactor.netty.channel.ChannelOperations;
 import reactor.netty.http.client.HttpClient;
 import reactor.netty.resources.ConnectionProvider;
 import reactor.test.StepVerifier;
@@ -186,6 +191,67 @@ class WebClientIntegrationTests {
 		});
 	}
 
+	@ParameterizedWebClientTest
+	void applyAttributesInNativeRequest(ClientHttpConnector connector) {
+		startServer(connector);
+		connector.setApplyAttributes(true);
+		checkAttributesInNativeRequest(true);
+	}
+
+	@ParameterizedWebClientTest
+	void dontApplyAttributesInNativeRequest(ClientHttpConnector connector) {
+		startServer(connector);
+		connector.setApplyAttributes(false);
+		checkAttributesInNativeRequest(false);
+	}
+
+	private void checkAttributesInNativeRequest(boolean expectAttributesApplied){
+		prepareResponse(response -> {});
+
+		final AtomicReference<Object> nativeRequest = new AtomicReference<>();
+		Mono<Void> result = this.webClient.get()
+				.uri("/pojo")
+				.attribute("foo","bar")
+				.httpRequest(clientHttpRequest -> nativeRequest.set(clientHttpRequest.getNativeRequest()))
+				.retrieve()
+				.bodyToMono(Void.class);
+		StepVerifier.create(result)
+				.expectComplete()
+				.verify();
+		if (nativeRequest.get() instanceof ChannelOperations<?,?> nativeReq) {
+			Attribute<Map<String, Object>> attributes = nativeReq.channel().attr(AttributeKey.valueOf("attributes"));
+			if (expectAttributesApplied) {
+				assertThat(attributes.get()).isNotNull();
+				assertThat(attributes.get()).containsEntry("foo", "bar");
+			}
+			else {
+				assertThat(attributes.get()).isNull();
+			}
+		}
+		else if (nativeRequest.get() instanceof reactor.netty5.channel.ChannelOperations<?,?> nativeReq) {
+			io.netty5.util.Attribute<Map<String, Object>> attributes = nativeReq.channel().attr(io.netty5.util.AttributeKey.valueOf("attributes"));
+			if (expectAttributesApplied) {
+				assertThat(attributes.get()).isNotNull();
+				assertThat(attributes.get()).containsEntry("foo", "bar");
+			}
+			else {
+				assertThat(attributes.get()).isNull();
+			}
+		}
+		else if (nativeRequest.get() instanceof Request nativeReq) {
+			if (expectAttributesApplied) {
+				assertThat(nativeReq.getAttributes()).containsEntry("foo", "bar");
+			}
+			else {
+				assertThat(nativeReq.getAttributes()).doesNotContainEntry("foo", "bar");
+			}
+		}
+		else if (nativeRequest.get() instanceof org.apache.hc.core5.http.HttpRequest nativeReq) {
+			// TODO get attributes from HttpClientContext
+		}
+	}
+
+
 	@ParameterizedWebClientTest
 	void retrieveJsonWithParameterizedTypeReference(ClientHttpConnector connector) {
 		startServer(connector);